Compensation optical apparatus and image sensing apparatus

ABSTRACT

A compensation optical apparatus for obtaining and image of an object without reduction in image quality irrespective of aberration compensation, includes: a division unit for dividing a return beam from a measured object; an aberration measurement unit for measuring an aberration caused by the measured object, with a divided beam from the division unit; an aberration compensation unit for performing aberration compensation based on the aberration measured by the aberration measurement unit; a projection unit for projecting a beam obtained by the aberration compensation in the aberration compensation unit to the measured object; an acquirement unit for acquiring a value exhibiting a state of the measured object based on the return beam from the measured object, which is obtained by the beam projected from the projection unit; and a control unit for retreating the division unit from an optical path based on the value acquired by the acquirement unit.

TECHNICAL FIELD

The present invention relates to a compensation optical apparatus and animage sensing apparatus including the compensation optical apparatus,for sensing an image of a measured object.

BACKGROUND ART

Major examples of an ophthalmologic image sensing apparatus are ascanning laser ophthalmoscope (SLO) and an optical coherence tomography(OCT) apparatus. Major examples of the OCT are a Time Domain OCT(TD-OCT) and a Spectral Domain OCT (SD-OCT).

In order to improve the resolution of a fundus image of an eye to beinspected, an attempt has been made to increase NA of a light projectionsystem for the eye to be inspected. Measuring light projected to thefundus passes through optical tissues of the eye to be inspected, suchas a cornea and a crystalline lens, and is affected by aberrations ofthe optical tissues. When the aberrations are large, there is a casewhere the quality of the fundus image is not improved by the increase inNA.

In view of the above, NPL 1 discloses an adaptive optics OCT (AO-OCT)which incorporates into the OCT an adaptive optics (AO) system in whichaberration measurement and aberration compensation are repeated at highspeed to pre-compensate for an aberration of the measuring light, whichis caused in the irradiated eye to be inspected, based on a measuredaberration.

In the AO-OCT, aberration of light obtained by dividing a return beamfrom the eye to be inspected is measured. Therefore, an intensity of thereturn beam to be used for the fundus image reduces, and hence thequality of the fundus image degrades. Even when the intensity of lightentering the eye to be inspected is increased in advance to compensatefor the reduction in intensity of the return beam which is caused by thedivision, there is a limit because the intensity of the incident lightis limited in under safety standards. Thus, it is necessary to minimizethe intensity of the light obtained by dividing the return beam foraberration measurement. On the other hand, in order to performaberration compensation in short time, short-time aberration measurementis required. Therefore, it is necessary to maximize the intensity oflight for aberration compensation.

CITATION LIST Non Patent Literature

-   NPL 1: Y. Zhang et al, Optics Express, Vol. 14, No. 10, May, 2006

SUMMARY OF INVENTION Technical Problem

The degree of improvement on image quality due to aberrationcompensation varies depending on a value exhibiting a state of ameasured object (also referred to as image sensing condition, forexample, aberration amount of anterior portion of eye to be inspected oraberration change amount thereof). When the intensity of the return beamreduces because of the division, the image quality after aberrationcompensation may be reduced to less than the image quality beforeaberration compensation, depending on the value.

Solution to Problem

A compensation optical apparatus according to the present inventionincludes; a division unit for dividing a return beam from a measuredobject, an aberration measurement unit for measuring an aberrationcaused by the measured object, with a divided beam from the divisionunit, an aberration compensation unit for performing aberrationcompensation based on the aberration measured by the aberrationmeasurement unit, a projection unit for projecting a beam obtained bythe aberration compensation in the aberration compensation unit to themeasured object, an acquirement unit for acquiring a value exhibiting astate of the measured object based on the return beam from the measuredobject, which is obtained by the beam projected from the projectionunit, and a control unit for retreating the division unit from anoptical path based on the value acquired by the acquirement unit.

Advantageous Effects of Invention

According to the compensation optical apparatus of the presentinvention, the unit for dividing a part of return beam based on thevalue exhibiting the state of the measured object (for example,aberration amount of anterior portion of eye to be inspected) to guidethe part of the return beam to the aberration measurement unit may beretreated. Therefore, even when image quality after aberrationcompensation becomes lower than image quality before aberrationcompensation, because an intensity of the return beam is not reduced bythe division, an image of the measured object may be obtained withoutthe reduction in image quality.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating a structural example of ascanning laser ophthalmoscope (SLO) used for a control method for anoptical image sensing apparatus according to a first embodiment of thepresent invention.

FIGS. 2A, 2B, 2C-1, 2C-2, 2D, 2E-1, and 2E-2 are schematic viewsillustrating a wavefront compensation device and a wavefront sensor inthe first embodiment of the present invention, in which FIG. 2A is aschematic view illustrating a reflection type liquid crystal opticalmodulator, FIG. 2B is a schematic diagram illustrating a variable shapemirror, FIGS. 2C-1 and 2C-2 are schematic views illustrating a structureof a Shack-Hartmann sensor, FIG. 2D is a schematic view illustrating astate in which a light beam for wavefront measurement is focused on aCCD sensor, and FIGS. 2E-1 and 2E-2 are schematic views illustrating acase where a wavefront having a spherical aberration is measured.

FIG. 3 is a flow chart illustrating a procedure of the control methodfor the optical image sensing apparatus according to the firstembodiment of the present invention.

FIGS. 4A, 4B, 4C and 4D illustrate examples of effects on image qualityin the present invention.

FIG. 5 is a flow chart illustrating a procedure of a control method foran optical image sensing apparatus according to a second embodiment ofthe present invention.

FIG. 6 is a schematic diagram illustrating a structural example of theSLO in a third embodiment of the present invention.

FIG. 7 is a flow chart illustrating a procedure of a control method foran optical image sensing apparatus according to the third embodiment ofthe present invention.

FIG. 8 is a schematic diagram illustrating a structural example of anoptical coherent tomography (OCT) apparatus in a fourth embodiment ofthe present invention.

DESCRIPTION OF EMBODIMENTS

According to a compensation optical apparatus of the present invention,a unit for dividing a part of return beam based on a value exhibiting astate of a measured object (for example, value exhibiting the quality ofan image including at least one of a resolution and an intensity,aberration amount of anterior portion of eye to be inspected, and changeamount of aberration) to guide the part of the return beam to anaberration measurement unit (division unit) may be retreated. Therefore,even when image quality after aberration compensation becomes lower thanimage quality before aberration compensation, because an intensity ofthe return beam is not reduced by the division, an image of the measuredobject may be obtained without the reduction in image quality.

The present invention is described with reference to the followingembodiments.

The present invention is not limited by the following structuresaccording to the respective embodiments.

First Embodiment

A first embodiment describes a structural example in which the presentinvention is applied to a scanning laser ophthalmoscope (SLO) providedwith a compensation optical function.

FIG. 1 is a schematic diagram illustrating a structural example of theSLO.

In FIG. 1, a light source 101 used in this embodiment is a superluminescent diode (SLD) light source having a wavelength of 840 nm.

The wavelength of the light source 101 is not particularly limited. Thewavelength of the light source 101 for fundus image sensing is suitablyset in a range of approximately 800 nm to 1,500 nm in order to reduceglare for a person to be inspected and maintain a resolution.

In this embodiment, the SLD light source is used. In addition to suchlight source, for example, a laser light source may be used.

In this embodiment, the light source is used in common for fundus imagesensing and wavefront measurement. A structure may be employed in whichrespective light sources are provided separately and light beamstherefrom are superimposed on each other on an optical path.

As illustrated in FIG. 1, light projected from the light source 101passes through a single-mode optical fiber 102, and is converted intocollimated light by a collimator 103 are projected.

Measuring light 105 projected from the collimator 103 passes through alight division portion 104 including a beam splitter and then enters aresolution setting unit 117.

The resolution setting unit 117 (also referred to as varying unit forvarying beam diameter or reducing beam diameter) varies the beamdiameter of the incident measuring light 105 to project the incidentmeasuring light 105, to thereby change an image sensing resolution.

When the beam diameter is varied in a range of approximately 7 mm to 1mm, the image sensing resolution on the fundus may be set in a range ofapproximately 3 μm to 20 μm.

It is useful to make the image sensing resolution variable, in order tolower the image sensing resolution to reduce a data amount when an imageis to be sensed at a wide viewing angle, in order to adjust the imagesensing resolution based on the aberration of the eye to be inspected,or in order to sense an image using a narrow beam passing around alow-transmittance portion depending on an image sensing method.

The resolution setting unit 117 is controlled by a resolution controller120. The resolution controller 120 operates in conjunction with acontrol unit 118.

The resolution setting unit 117 suitably has a structure includingmultiple lenses to adjust a positional relationship therebetween, andmay have a structure for continuously changing a resolution or astructure for discretely changing a resolution.

The measuring light 105 passing through the resolution setting unit 117is guided to a compensation optical system.

The compensation optical system includes a light division portion(corresponding to division unit in this embodiment) 106, a wavefrontsensor (corresponding to aberration measurement unit in this embodiment)115, a wavefront compensation device (corresponding to aberrationcompensation unit in this embodiment) 108, and reflective mirrors 107-1to 107-4 for guiding the measuring light 105 to those components. Thelight division portion 106 and the wavefront sensor 115 are provided ona stage (not shown) to be inserted into an optical path of the measuringlight 105 as described later.

The reflective mirrors 107-1 to 107-4 are provided so that at least apupil of the eye, the wavefront sensor 115, and the wavefrontcompensation device 108 are in an optically conjugate relationship. Inthis embodiment, a beam splitter is used as the light division portion106.

The measuring light 105 passing through the light division portion 106enters the wavefront compensation device 108.

The measuring light 105 reflected on the wavefront compensation device108 travels to the reflective mirror 107-3.

In this embodiment, a spatial phase modulator including a liquid crystalelement is used as the wavefront compensation device 108.

FIG. 2A is a schematic view illustrating a reflection type liquidcrystal optical modulator used as an example of the spatial phasemodulator in this embodiment.

The reflection type liquid crystal optical modulator has a structure inwhich liquid crystal molecules 125 are filled into a space surrounded bya base portion 122 and a cover 123.

The base portion 122 includes multiple pixel electrodes 124. The cover123 includes a transparent counter electrode (not shown).

When no voltages are applied between the pixel electrodes and thecounter electrode, the liquid crystal molecules are in such anorientation state as the liquid crystal molecules 125-1. When voltagesare applied, the orientation state is changed to such an orientationstate as the liquid crystal molecules 125-2, and hence a refractiveindex with respect to incident light changes.

When a voltage is controlled for each of the pixel electrodes to changea refractive index of each pixel, spatial phase modulation may berealized.

For example, when incident light 126 enters the liquid crystal element,light passing through the liquid crystal molecules 125-2 is delayed inphase from light passing through the liquid crystal molecules 125-1, tothereby form a wavefront 127 as illustrated in FIG. 2A.

The reflection type liquid crystal optical modulator generally includesseveral ten thousand to several hundred thousand pixels. The liquidcrystal element has a polarization characteristic, and hence thereflection type liquid crystal optical modulator may include apolarization element for adjusting a polarization state of incidentlight.

Another example of the wavefront compensation device 108 is a variableshape mirror.

The variable shape mirror may locally change a light reflectiondirection, and various types of variable shape mirrors are put intopractical use.

For example, there is a device as illustrated in a cross section view ofFIG. 2B.

The device includes: a film-shaped mirror surface 129 which reflectsincident light and is deformable; a base portion 128; actuators 130interposed between the mirror surface 129 and the base portion 128; anda support portion (not shown) for supporting the periphery of the mirrorsurface 129.

The operational principles of the actuators 130 may be based on anelectrostatic force, a magnetic force, or a piezoelectric effect. Astructure of the actuators 130 varies depending on the operationalprinciples.

The multiple actuators 130 are two-dimensionally arranged on the baseportion 128 and selectively driven to be able to freely deform themirror surface 129. The variable shape mirror generally includes severalten to several hundred actuators.

The light reflected on the reflective mirrors 107-3 and 107-4 isone-dimensionally or two-dimensionally scanned by a scanning opticalsystem 109.

In this embodiment, two galvano-scanners are used as the scanningoptical system 109 for main scanning (lateral direction of fundus) andsub scanning (longitudinal direction of fundus).

In order to sense an image at a higher speed, a resonance scanner may beused for the main scanning side of the scanning optical system 109.

In order to bring the respective scanners included in the scanningoptical system 109 into an optically conjugate relationship, opticalelements such as a mirror and a lens may be used between the respectivescanners depending on a structure.

The measuring light 105 scanned by the scanning optical system 109 isprojected to an eye 111 through eyepieces 110-1 and 110-2 serving as aneyepiece portion.

The measuring light projected to the eye 111 is reflected or scatteredon the fundus to become a return beam. When the eyepieces 110-1 and110-2 are adjusted in position, suitable projection may be performedaccording to the diopter of the eye 111.

The lenses are used for the eyepiece portion in this embodiment, but,for example, spherical mirrors may be used.

Reflected scattering light of the return beam which is produced byreflection or scattering on a retina of the eye 111 travels in thereverse direction on the same optical path as in the case of incidence.A part of the reflected scattering light is reflected by the lightdivision portion 106 to the wavefront sensor 115 to be used formeasuring a light beam wavefront.

In this embodiment, a Shack-Hartmann sensor is used as the wavefrontsensor 115. The Shack-Hartmann sensor receives the reflected lightresulting from the measuring light entering the eye by a CCD camerathrough a micro-lens array, to measure a wavefront.

The wavefront compensation device, for example, the variable shapemirror or the spatial phase modulator is driven so as to compensate forthe measured wavefront to sense an image of the fundus through thedevice, and hence high-resolution image sensing may be achieved.

FIG. 2C-1 is a schematic view illustrating the Shack-Hartmann sensor.

A light beam 131 for wavefront measurement is focused on a focal surface134 of a CCD sensor 133 through a micro-lens array 132.

FIG. 2C-2 illustrates a state as viewed from a position indicated by2C-2-2C-2 of FIG. 2C-1. The micro-lens array 132 includes multiplemicro-lenses 135. The light beam 131 is focused on the CCD sensor 133through the respective micro-lenses 135, and hence the light beam 131 isdivided into spots equal in number to the micro-lenses 135 to form thespots.

FIG. 2D illustrates a state in which the spots are formed on the CCDsensor 133. The light beam passing through the respective micro-lenses135 is focused to form spots 136. A wavefront of the incident light beamis calculated based on the positions of the respective spots 136.

For example, FIG. 2E-1 is a schematic view illustrating a case where awavefront having a spherical aberration is measured.

The light beam 131 is formed to have a wavefront 137.

The light beam 131 is focused at positions in a direction of the localnormal to the wavefront by the micro-lens array 132.

A focal state on the CCD sensor 133 in this case is illustrated in FIG.2E-2.

The light beam 131 has a spherical aberration, and hence the formedspots 136 are biased to the central portion. When the positions of theformed spots 136 are calculated, the wavefront of the light beam 131 maybe determined. In this embodiment, the Shack-Hartmann sensor is used asthe wavefront sensor. However, the present invention is not limited tothis sensor. Another wavefront measurement unit, for example, acurvature sensor may be employed or a method of obtaining the wavefrontby reverse calculation from the formed spot images may be employed.

When the reflected scattering light passes through the light divisionportion 106, a part thereof is reflected on the light division portion104 and is guided to a light intensity sensor 114 through a collimator112 and an optical fiber 113.

The light intensity sensor 114 converts the light into an electricalsignal. The electrical signal is processed by the control unit 118 intoan image as a fundus image and the fundus image is displayed on adisplay 119.

The wavefront sensor 115 is connected to a compensation opticalcontroller 116. The received wavefront is transferred to thecompensation optical controller 116.

The wavefront compensation device 108 is also connected to thecompensation optical controller 116 and performs modulation instructedfrom the compensation optical controller 116.

The compensation optical controller 116 calculates a modulation amountfor compensation to obtain wavefront having no aberration based on thewavefront obtained by the wavefront sensor 115, and instructs thewavefront compensation device 108 to perform the compensation accordingto the modulation amount.

The wavefront measurement and the instruction to the wavefrontcompensation device are repeated and feedback control is performed toalways obtain a suitable wave front.

For aberration compensation, it is necessary to divide a part of signallight by the light division portion 106 to measure the wavefront.

A feature of this embodiment is as follows. The effectiveness ofcompensation, that is, whether or not an effect obtained by continuouscompensation using the adaptive optics (AO) exceeds, even during imagesensing, the influence of the reduction in image sensing light amount,which is caused by the division is determined, and the division, is madewhen the effect exceeds the influence.

In this embodiment, the beam splitter having a division ratio of 80(transmission):20 (reflection) is used as the light division portion106. Therefore, when light is divided in order to measure the wavefrontby the wavefront sensor 115, the fundus image sensing light amount isreduced by 20%.

When an image quality improvement effect obtained by aberrationcompensation exceeds the influence of the light amount reduced by 20%,the compensation is performed even while the image of the fundus issensed.

The light division portion 106 is inserted into the optical path of themeasuring light 105 to perform optical path division.

Next, a procedure of a control method for an optical image sensingapparatus according to this embodiment is described with reference to aflow chart illustrated in FIG. 3.

First, in Step S101, control processing starts.

Next, in Step S102, a resolution is set.

To be specific, the control unit 118 controls the resolution settingunit 117 through the resolution controller 120 and adjusts the beamdiameter of the measuring light to set the resolution.

Next, in Step S103, for aberration compensation, the light divisionportion 106 is inserted into the optical path of the measuring light 105under the control of the control unit 118 to divide light to thewavefront sensor. In next Step S104 and subsequent steps, processingusing the compensation optical system is performed.

In the fundamental flow for the compensation optical system, while thelight is divided to the wavefront sensor 115 by the light divisionportion 106 (also referred to as division unit), an aberration ismeasured by the wavefront sensor 115 in Step S104.

Next, in Step S106, a compensation amount is calculated by thecompensation optical controller 116 based on a result obtained by themeasurement.

Next, in Step S107, the wavefront compensation device 108 is drivenunder the control of the compensation optical controller 116. Theabove-mentioned flow is repeated as the processing using thecompensation optical system.

During this flow, after the aberration is measured in Step S104, whetheror not the aberration amount is smaller than a preset reference value isdetermined by the compensation optical controller 116 in Step S105.

The reference value may be a value specific to the apparatus or may beset by a photographer.

When the aberration amount exceeds the reference value, Step S106 andsubsequent processings are executed.

On the other hand, when the aberration amount is smaller than thereference value, the processing proceeds to Step S108.

In Step S108, whether or not the image quality is to be improved by thecontinuous aberration compensation even when the light amount loss is20% as described above is determined.

In this embodiment, two parameters of resolution and image sensingsignal intensity are used to determine whether or not the image qualityis to be improved.

The aberration compensation causes the increase in resolution. The imagequality improves with the improvement of light receiving efficiency. Incontrast to this, a light receiving amount is reduced by 20% because ofthe division. The image quality reduces with the reduction in lightreceiving amount.

Therefore, whether or not the image quality is to be finally improved isdetermined based on both the parameters.

The determination is made by the control unit 118 for controlling theSLO in this embodiment. The control unit 118 may include a computersystem.

Examples of the determination are described with reference to FIGS. 4Ato 4D.

FIGS. 4A and 4B illustrate examples in which whether or not the imagequality is to be improved is determined based on only the signalintensity.

FIG. 4A illustrates an initial signal intensity 138-1 in the case whereaberration compensation is not performed. When the measuring light isdivided for aberration measurement, the light receiving amount isreduced by 20% and the signal intensity is reduced from the initialsignal intensity 138-1 to a signal intensity 138-2.

Note that, when the aberration compensation is performed, the lightreceiving efficiency is improved to increase the signal intensity, andhence the signal intensity is increased to a signal intensity 138-3.

That is, the signal intensity 138-3 in the case where the compensationis performed exceeds the signal intensity 138-1 in the case where thecompensation is not performed, and hence it is determined that the imagequality is to be improved by the continuous compensation.

In contrast to this, FIG. 4B illustrates the case where the signalintensity is not expected to be increased by the compensation. As in thecase illustrated in FIG. 4A, beam division is performed forcompensation, and hence the light receiving intensity is reduced from aninitial signal intensity 139-1 to a signal intensity 139-2.

The signal intensity is increased by the compensation, but an effectobtained by the compensation is small and the signal intensity is onlyincreased to a signal intensity 139-3. In this case, the signalintensity 139-3 is lower than the initial signal intensity 139-1 andthus the image quality is reduced, and hence there is no merit incontinuing the compensation. Therefore, it is determined not to performthe compensation.

Next, examples in which whether or not the image quality is to beimproved is determined based on the signal intensity and the resolutionare described with reference to FIGS. 4C and 4D.

FIG. 4C illustrates an initial signal intensity-resolution point 140-1in the case where the compensation is not performed. Even when themeasuring light is divided for aberration measurement, the resolution isnot reduced and only the light receiving amount is reduced, and hencethe signal intensity-resolution point is shifted to a signalintensity-resolution point 140-2.

When the compensation is performed, the light receiving efficiency isimproved to increase the signal intensity and the resolution isimproved, and hence the signal intensity-resolution point is shifted toa signal intensity-resolution point 140-3.

Whether or not the image quality is to be improved is determined basedon the combination of the signal intensity and the resolution.Therefore, a threshold value (indicated by broken line) 141 asillustrated in FIGS. 4C and 4D is set as a reference to determinewhether or not the image quality is to be improved.

When the signal intensity-resolution point 140-3 is compared with theinitial signal intensity-resolution point 140-1, the signal intensity isnot significantly increased but the resolution is improved, and hencethe signal intensity-resolution point 140-3 exceeds the threshold valueas the reference for determination.

Therefore, it is determined that there is a compensation effect.

On the other hand, in FIG. 4D, the signal intensity is reduced by beamdivision to shift an initial signal intensity-resolution point 142-1 toa signal intensity-resolution point 142-2. When the compensation isperformed, the signal intensity-resolution point 142-2 is shifted to thesignal intensity-resolution point 142-3 to improve the signal intensityand the resolution.

However, the signal intensity-resolution point 142-3 does not reach tothe threshold value as the reference for determination, and hence it isdetermined that there is no compensation effect.

Whether or not the signal intensity and the resolution are to beimproved by the compensation may be determined based on, for example,the beam diameter for sensing the image of the fundus, the change inlight amount which is caused by the compensation, aberration data of themeasured eye, the performance of the compensation device, an imagesensing time, and a temporal change in aberration.

An image quality threshold value for a combination of the signalintensity and the resolution may be determined based on the signalintensity and the resolution which are weighted. A weighting ratio ischanged depending on an image to be obtained. For example, a mode whichis suitable for high-magnification image sensing and used to improve theresolution having priority over the signal intensity and a mode which issuitable for wide-angle image sensing and used to improve the signalintensity having priority over the resolution may be set and selected byan operator.

In FIGS. 4C and 4D, the threshold value is set to include the initialvalue of the image quality. The threshold value may be set to obtainhigher image quality than that of the initial value depending on thedegree of desired image quality.

When it is determined in Step S108 that the compensation effect exceedsthe light amount loss caused by beam division, the processing proceedsto Step S117. When it is determined that the compensation effect doesnot exceed the light amount loss, the processing proceeds to Step S109and beam division to the wavefront sensor 115 is canceled (division unitis retreated).

Next, a shape of the compensation device 108 in the case where the beamdivision to the wavefront sensor 115 is canceled is described.

When the beam division is canceled in Step S109, the shape of thecompensation device 108 is held to a shape immediately before canceling.

Therefore, division loss may be suppressed while the aberrationcompensation effect is maintained to some extent.

The compensation device 108 may be set in an initial device state. Inthis case, the wavefront compensation is not affected by the aberrationcompensation.

In Step S110, image sensing is performed. In Step S111, whether or notan image sensing completion request is received is confirmed. When theimage sensing completion request is not received, processing returns toStep S110 and the image sensing is performed again. When the imagesensing completion request is received, the processing proceeds to StepS112 and the control processing is ended.

When the processing proceeds to Step S117, image sensing is performed inStep S117. In Step S118, whether or not the image sensing is completedis confirmed.

When the image sensing completion request is not received, theprocessing of Steps S113 to S116 using the compensation optical systemis performed, and then the image sensing is performed again in StepS117.

In this embodiment, the image sensing and the aberration compensationprocessing are sequentially performed, but may be performed in parallel.

When the image sensing completion request is confirmed in Step S118, thebeam division is canceled in Step S119 and the control processing isended in Step S112.

As described above, according to this embodiment, the operation of thecompensation optical system may be suitably controlled depending onimage sensing conditions.

Suitable aberration compensation corresponding to image sensingconditions may be executed, and hence high-quality fundus image sensingmay be achieved and image quality may be prevented from being reduced byaberration compensation.

When it is determined that there is no aberration compensation effect,the division of aberration measurement light which becomes waste lightmay be canceled.

Second Embodiment

A second embodiment describes a different structural example, from thefirst embodiment, in which the present invention is applied to an SLO.

An optical image sensing apparatus according to this embodiment has thesame structure as in the first embodiment illustrated in the schematicdiagram of FIG. 1.

Next, a procedure of a control method for the optical image sensingapparatus according to this embodiment is described with reference to aflow chart illustrated in FIG. 5.

This embodiment has a feature in that a threshold value of a beamdiameter for which dynamic aberration compensation is required is set inadvance, and whether or not beam division for aberration measurement isperformed is determined based on a measured beam diameter.

First, in Step S101, control processing starts.

Next, in Step S102, a resolution is set.

Next, in Step S103, for aberration compensation, the light divisionportion 106 is inserted into the optical path of the measuring light 105to divide the light to the wavefront sensor 115.

In next Step S104 and subsequent steps, processing using thecompensation optical system is performed.

The fundamental flow for the compensation optical system is the same asin the first embodiment, and Steps S104 to S107 are repeated while thelight is divided to the wavefront sensor 115 by the light divisionportion 106.

During this flow, after the aberration is measured in Step S104, whetheror not the aberration amount is smaller than a preset reference value isdetermined by the compensation optical controller 116 in Step S105.

When the aberration amount exceeds the reference value, Step S106 andsubsequent processings are executed.

On the other hand, when the aberration amount is smaller than thereference value, the processing proceeds to Step S120.

In Step S120, whether or not a measured beam diameter exceeds thethreshold value of the beam diameter for which dynamic aberrationcompensation is required is determined.

When the measured beam diameter is large, the influence of aberration onimage quality is large, and hence the aberration compensation effect islarge.

In contrast to this, when the measured beam diameter is small, the imagequality is not significantly improved even by aberration compensation,and hence a light receiving amount loss caused by beam division becomeslarger.

Therefore, whether or not the dynamic aberration compensation isrequired may be determined based on the measured beam diameter.

The threshold value of the beam diameter for which the dynamicaberration compensation is required may be calculated based on generalaberration information of the eye and compensation performance of theapparatus, or may be calculated based on measured aberration informationof the eye to be measured in addition to the general aberrationinformation and the compensation performance.

When the measured beam diameter exceeds the threshold value, theprocessing proceeds to Step S117. When the measured beam diameter doesnot exceed the threshold value, the processing proceeds to Step S109.

In Step S109, beam division to the wavefront sensor 115 is canceled. InStep S110, image sensing is performed.

In Step S111, whether or not the image sensing completion request isreceived is determined. When the image sensing completion request is notreceived, processing returns to Step S110 and the image sensing isperformed again. When the image sensing completion request is received,the processing proceeds to Step S112 and the control processing isended.

When the processing proceeds to Step S117, image sensing is performed.In Step S118, whether or not the image sensing is completed isdetermined.

When the image sensing completion request is not received, theprocessing of Steps S113 to S116 using the compensation optical systemis performed, and then the image sensing is performed again in StepS117.

In this embodiment, the image sensing and the aberration compensationprocessing are sequentially performed, but may be performed in parallel.

When the image sensing completion request is confirmed in Step S118, thebeam division is canceled in Step S119 and the control processing isended in Step S112.

As described above, according to this embodiment, the operation of thecompensation optical system may be suitably controlled depending onimage sensing conditions.

Aberration compensation suited to image sensing conditions may beexecuted, and hence high-quality fundus image sensing may be achievedand image quality may be prevented from being reduced by aberrationcompensation. In particular, the effectiveness of aberrationcompensation is determined based on the predetermined value, and hence acalculation load may be reduced.

Third Embodiment

A third embodiment describes a different structural example, from thefirst and second embodiments, in which the present invention is appliedto a SLO, with reference to FIG. 6.

An optical image sensing apparatus according to this embodiment hasfundamentally the same structure as in the first embodiment illustratedin the schematic diagram of FIG. 1, but does not include the resolutionsetting unit 117. Therefore, measurement is performed at a specificresolution.

Next, a procedure of a control method for the optical image sensingapparatus according to this embodiment is described with reference to aflow chart illustrated in FIG. 7.

This embodiment has a feature in that an image quality improvementeffect by dynamic compensation is determined based on a temporalfluctuation in aberration measured during aberration compensation.

First, in Step S101, control processing starts.

Next, in Step S103, for aberration compensation, the light divisionportion 106 is inserted into the optical path of the measuring light 105to divide the light to the wavefront sensor 115.

In next Step S104 and subsequent steps, processing using thecompensation optical system is performed.

The fundamental flow for the compensation optical system is the same asin the first embodiment. Steps S104, S121, S105, S106, and S107 arerepeated while the light is divided to the wavefront sensor 115 by thelight division portion 106.

After an aberration is measured in Step S104, the measured aberrationdata is recorded in a recording apparatus (not shown) in Step S121.

In Step S105, whether or not the measured aberration amount is smallerthan a preset reference value is determined by the compensation opticalcontroller 116. When the aberration amount exceeds the reference value,Step S106 and the subsequent processing are executed.

On the other hand, when the aberration amount is smaller than thereference value, the processing proceeds to Step S122.

In Step S122, a temporal fluctuation in aberration is calculated basedon the aberration data recorded in Step S121, and whether or not thetemporal fluctuation exceeds a threshold value is determined.

When the temporal fluctuation is large, an aberration is likely togreatly fluctuate during fundus image sensing, to thereby significantlyreduce image quality, and hence dynamic aberration compensation isnecessary.

In contrast to this, when an aberration fluctuation amount is small andthus aberration does not greatly fluctuate, the aberration is expectednot to greatly fluctuate even during fundus image sensing, and hence thedynamic aberration compensation is determined to be unnecessary.

When the fluctuation in aberration exceeds the threshold value, theprocessing proceeds to Step S117. When it is determined that thefluctuation in aberration does not exceed the threshold value, theprocessing proceeds to Step S109.

In Step S109, division control is performed so that the light divisionportion located on an optical path of the return beam is retreated(removed) from the optical path to cancel the beam division to thewavefront sensor 115. In Step S110, image sensing is performed.

In Step S111, whether or not an image sensing completion request isreceived is determined. When the image sensing completion request is notreceived, processing returns to Step S110 and the image sensing isperformed again. When the image sensing completion request is received,the processing proceeds to Step S112 and the control processing isended.

When the processing proceeds to Step S117, image sensing is performed.In Step S118, whether or not the image sensing is completed isdetermined.

When the image sensing completion request is not received, theprocessing of Steps S113 to S116 using the compensation optical systemis performed, and then the image sensing is performed again in StepS117.

In this embodiment, the image sensing and the aberration compensationprocessing are sequentially performed, but may be performed in parallel.

When the image sensing completion request is confirmed in Step S118, thebeam division is canceled in Step S119 and the control processing isended in Step S112.

As described above, according to this embodiment, the operation of thecompensation optical system may be suitably controlled depending onimage sensing conditions.

Aberration compensation suited to image sensing conditions may beexecuted, and hence high-quality fundus image sensing may be achievedand image quality may be prevented from being reduced by aberrationcompensation.

In particular, the influence on actual image quality is considered, andhence the effectiveness may be more accurately determined.

Fourth Embodiment

A fourth embodiment describes a structural example in which the presentinvention is applied to an optical coherent tomography (OCT) apparatusprovided with a compensation optical function.

FIG. 8 is a schematic diagram illustrating a structural example of theOCT.

In FIG. 8, the light source 101 used in this embodiment is an SLD lightsource having a wavelength of 840 nm.

The light source 101 desirably has low coherence. An SLD having awavelength width equal to or longer than 30 nm is suitably used. Anultra-short pulse laser, for example, a titanium sapphire laser may beused as the light source.

Light projected from the light source 101 is guided to a fiber coupler143 through the single-mode optical fiber 102.

An optical path is divided by the fiber coupler 143 into a signal lightpath 144 and a reference light path 145. The fiber coupler to be usedhas a division ratio of 10:90 and is provided so that 10% of theprojected light travels on the signal light path 144.

The light traveling on the signal light path 144 is converted intocollimated light by the collimator 103.

The collimator 103 and the subsequent elements are the same as in thefirst embodiment. The light is projected to the eye 111 through thecompensation optical system and the scanning optical system.

Reflected scattering light from the eye 111 travels along the same pathagain and is guided through the optical fiber (signal light path) 144 toreach the fiber coupler 143.

In this embodiment, the resolution setting unit 117 is provided closerto the eye with respect to the light division portion 106. Therefore,even when a resolution is adjusted, a beam diameter of light enteringthe wavefront sensor 115 is not changed.

In contrast to this, reference light traveling on the reference lightpath 145 exits from a collimator 146 to be reflected on an optical pathlength varying portion 147, and returns to the fiber coupler 143 again.

The signal light and the reference light which reach the fiber coupler143 are superimposed on each other and guided to a spectroscope 149through an optical fiber 148.

A tomographic image of the fundus is formed by the control unit 118based on interference light information obtained by the spectroscope149.

The control unit 118 may control the optical path length varying portion147 to obtain an image at a desired depth position.

As in the first embodiment, a wavefront is measured by the wavefrontsensor 115 and the wavefront compensation device 108 is driven to cancelan aberration of the wave front.

Even in this embodiment, processing is performed through the stepsillustrated in FIG. 3 as in the first embodiment. When it is determinedthat the image quality is to be improved by the aberration compensation,the image sensing of the fundus is performed during the dynamicaberration compensation.

The tomographic image is obtained by the OCT. However, when an NA ofincident light is increased to improve the resolution, a depth of fieldbecomes shallower, and hence the tomographic image includes a focusedregion and a non-focused region.

Therefore, it is conceivable to employ a method of dividing an imagesensing region in a depth direction by a width corresponding to thedepth of field to perform image sensing and then combining images atrespective depths to obtain a tomographic image focused on the entireregion.

In this case, a region in the depth direction which is obtained by eachimage sensing is adjusted according to the resolution changed in StepS102 illustrated in FIG. 3, and hence an image having a large focusedregion may be easily sensed at high speed.

As described above, according to this embodiment, the operation of thecompensation optical system may be suitably controlled based on theimage sensing conditions.

A suitable aberration compensation method may be executed even for thetomographic image of the fundus, and hence the high-quality tomographicimage of the fundus may be obtained and the reduction in image qualitymay be prevented.

With respect to the control method for the optical image sensingapparatus according to each of the embodiments as described above,programs for causing a computer to execute the control method may beproduced and stored in a storage medium to be read by the computer.

Other Embodiments

Aspects of the present invention can also be realized by a computer of asystem or apparatus (or devices such as a CPU or MPU) that reads out andexecutes a program recorded on a memory device to perform the functionsof the above-described embodiment(s), and by a method, the steps ofwhich are performed by a computer of a system or apparatus by, forexample, reading out and executing a program recorded on a memory deviceto perform the functions of the above-described embodiment(s). For thispurpose, the program is provided to the computer for example via anetwork or from a recording medium of various types serving as thememory device (e.g., computer-readable medium).

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2010-019120, filed Jan. 29, 2010, which is hereby incorporated byreference herein in its entirety.

The invention claimed is:
 1. A compensation optical apparatus,comprising: a division unit for dividing a return beam from a measuredobject; an aberration measurement unit for measuring an aberrationcaused by the measured object, with a divided beam from the divisionunit; an aberration compensation unit for performing aberrationcompensation based on the aberration measured by the aberrationmeasurement unit; a projection unit for projecting a beam obtained bythe aberration compensation in the aberration compensation unit to themeasured object; an acquirement unit for acquiring a value exhibiting astate of the measured object based on the return beam from the measuredobject, which is obtained by the beam projected from the projectionunit; and a control unit for retreating the division unit from anoptical path based on the value acquired by the acquirement unit.
 2. Acompensation optical apparatus according to claim 1, wherein: the valueexhibiting the state of the measured object comprises an amount of theaberration measured by the aberration measurement unit; and the controlunit retreats the division unit from the optical path when the amount ofthe aberration is equal to or larger than a predetermined aberrationamount.
 3. A compensation optical apparatus according to claim 1,further comprising a varying unit for varying a beam diameter of thebeam obtained by the aberration compensation in the aberrationcompensation unit, wherein: the value exhibiting the state of themeasured object comprises the beam diameter of the beam obtained by theaberration compensation in the aberration compensation unit; and thecontrol unit retreats the division unit from the optical path when thebeam diameter varied by the varying unit is smaller than a predetermineddiameter.
 4. A compensation optical apparatus according to claim 3,wherein the varying unit reduces the beam diameter of the beam obtainedby the aberration compensation in the aberration compensation unit whenan amount of the aberration measured by the aberration measurement unitis equal to or larger than a predetermined aberration amount.
 5. Acompensation optical apparatus according to claim 1, wherein: the valueexhibiting the state of the measured object comprises a fluctuationamount of the aberration measured by the aberration measurement unit;and the control unit retreats the division unit from the optical pathwhen the fluctuation amount is smaller than a predetermined fluctuationamount.
 6. An image sensing apparatus for sensing an image of a measuredobject, comprising: the compensation optical apparatus according toclaim 1; and an image acquirement unit for acquiring the image of themeasured object based on the return beam from the measured object undera state in which a compensation characteristic obtained by theaberration compensation unit is maintained and the division unit isretreated from the optical path.
 7. An image sensing apparatus forsensing an image of a measured object, comprising: the compensationoptical apparatus according to claim 1; and an image acquirement unitfor acquiring the image of the measured object based on a part of thereturn beam from the measured object under a state in which the divisionunit is inserted into the optical path during the aberrationcompensation performed by the aberration compensation unit.
 8. An imagesensing apparatus for sensing an image of a measured object, comprising:the compensation optical apparatus according to claim 1; and an imageacquirement unit for acquiring the image of the measured object based onthe return beam from the measured object, wherein: the value exhibitingthe state of the measured object comprises a value exhibiting quality ofthe image; and the control unit retreats the division unit from theoptical path when the value exhibiting the quality of the image issmaller than a predetermined value.
 9. An image sensing apparatusaccording to claim 8, wherein the control unit retreats the divisionunit from the optical path when a value exhibiting quality of an imageobtained under a state in which the division unit is retreated from theoptical path is larger than a value exhibiting quality of an imageobtained under a state in which the division unit is inserted into theoptical path.
 10. An image sensing apparatus according to claim 8,wherein the value exhibiting the quality of the image comprises at leastone of a resolution and an intensity.
 11. A compensation opticalapparatus, comprising: an aberration measurement unit for measuring anaberration caused by a measured object based on a return beam from themeasured object; an aberration compensation unit for compensating anaberration in accordance with the aberration measured by the aberrationmeasurement unit; a projection unit for projecting onto the measuredobject a beam compensated by the aberration compensation unit; and adivision unit capable of being inserted into and retreated from anoptical path of the beam projected from the projection unit, fordividing the return beam from the measured object caused from theprojected beam, and guiding a part of the return beam into theaberration measurement unit.
 12. A compensation optical apparatusaccording to claim 11, further comprising a control unit for retreatingthe division unit from the optical path in accordance with an aberrationamount measured by the aberration measurement unit.
 13. A compensationoptical apparatus according to claim 12, wherein the control unitretreats the division unit from the optical path in a case that theaberration amount is equal to or less than a predetermined value.
 14. Animage sensing apparatus for sensing an image of the measured object,comprising: the compensation optical apparatus according to claim 12;and an image acquirement unit for acquiring the image of the measuredobject based on the return beam from the measured object in accordancewith the retreating the division unit.
 15. An image sensing apparatusfor sensing an image of the measured object, comprising: thecompensation optical apparatus according to claim 12; and an imageacquirement unit for acquiring the image of the measured object based onthe return beam from the measured object under a state in which acompensation characteristic obtained by the aberration compensation unitis maintained and the division unit is retreated from the optical path.